The present invention relates to an image-forming optical system and, more particularly, to a compact reflecting decentered image-forming optical system. The present invention also relates to an image read apparatus using such an image-forming optical system. More particularly, the present invention relates to an image read apparatus used to enable an image pickup apparatus to image an information recording medium, e.g. a sheet of paper, a resin film, or a metal sheet, which contains the record of optically readably encoded multimedia information. The present invention also relates to an information reproducing system using the image read apparatus.
There has heretofore been known a compact reflecting decentered optical system as disclosed in Japanese Patent Application Unexamined Publication Number [hereinafter referred to as "JP(A)"] 59-84201. This is an invention of a one-dimensional light-receiving lens comprising a cylindrical reflecting surface; therefore, two-dimensional imaging cannot be effected with this conventional optical system. JP(A) 62-144127 discloses an optical system wherein the identical cylindrical surface is used twice to effect reflection in order to reduce spherical aberration in the above-mentioned invention.
JP(A) 62-205547 discloses the use of an aspherical reflecting surface as a reflecting surface, but makes no mention of the configuration of the reflecting surface. U.S. Pat. Nos. 3,810,221 and 3,836,931 both disclose an example in which a rotationally symmetric aspherical mirror and a lens system having a surface which has only one plane of symmetry are used to constitute a finder optical system of a reflex camera. In this example, however, the surface having only one plane of symmetry is utilized for the purpose of correcting the tilt of a virtual image for observation.
JP(A) 1-257834 (U.S. Pat. No. 5,274,406) discloses an example in which a surface having only one plane of symmetry is used for a reflecting mirror to correct image distortion in a rear projection type television. In this example, however, a projection lens system is used for projection onto a screen, and the surface having only one plane of symmetry is used for correction of image distortion.
JP(A) 7-333551 discloses an example of a back-coated mirror type decentered optical system using an anamorphic surface and a toric surface as an observation optical system. However, the decentered optical system is not sufficiently corrected for aberrations, including image distortion.
None of the above-described prior arts use a surface having only one plane of symmetry as a back-coated mirror to form a folded optical path.
Incidentally, as mediums for recording audio information such as speech and music, various mediums are known in addition to magnetic tapes and optical disks. However, the unit costs of these mediums are high to some extent even when they are mass-replicated. Moreover, the audio information recording mediums require some space for storage. To hand a speech-recorded medium to a person in a remote place, someone will take it with him or her, or the medium will be mailed. Accordingly, it takes some time for the medium to reach the person in the remote place. The same is true of information other than audio information, for example, image information obtained from cameras, video equipment, etc., and digital code data obtained from personal computers, word processors, etc.
In view of these circumstances, the present applicant has proposed an information processing system in JP(A) 6-231466. According to the information processing system, multimedia information, e.g. audio information such as speech or music, image information obtained from a camera, video equipment, etc., or digital code data obtained from a personal computer, a word processor, etc., is recorded on a resin film, a metal sheet or the like in the form of optically readable code information (image), e.g. an encoded dot pattern. To read the information recording medium having the multimedia information recorded thereon, illuminating light is applied to the dot pattern, and the reflected light from the dot pattern is read and processed by using an optical device, thereby reproducing the recorded multimedia information.
In the information processing system, multimedia information is recorded on a sheet of paper, which is considered to be the most economical medium, or a sheet-shaped medium that is equivalent to it. The use of such sheet-shaped mediums is considerably useful for achieving low-cost and space-saving mediums. Information that is recorded in the form of dot patterns can be readily transmitted by facsimile. Thus, information can be readily transferred to a person residing in a remote place. This is particularly significant for speech information. That is, the information processing system enables the exchange of speech information, which has heretofore been made by the delivery of a medium itself, to be carried out instantaneously and easily with a person residing in a distant place by facsimile.
However, the conventional technology suffers from problems as stated below. To construct a distortion-free image-forming optical system having a wide field angle and satisfactorily corrected for aberrations, if a rotationally symmetric optical system is used, the number of lens constituent elements becomes undesirably large, and the resulting optical system inevitably becomes large in size and costly.
Incidentally, JP(A) 6-231466 shows a pen-type information reproducing apparatus as a form of information reproducing apparatus [for example, see FIG. 41(B) of the publication].
However, the pen-type information reproducing apparatus suffers from some problems. The first problem is concerned with mounting of electric boards. Regarding the layout (mounting) of the interior of an information reproducing apparatus, it is preferable from the viewpoint of minimizing the number of boards that, as shown in FIG. 31, electric boards 91 and 91' equipped with an image processing unit, a data processing unit, an image pickup device 92, etc. should be disposed in the longitudinal direction of the pen and approximately parallel to a casing 90. In this case, however, the image pickup device 92 is disposed approximately perpendicular to the electric board 91 under the necessity of lying face-to-face with an information recording medium 100. Therefore, it is difficult to make the boards 91 and 91' common to each other. This gives rise to problems in terms of mounting efficiency and cost. It is possible to bend the optical path by adding optical members, e.g. mirrors, to an optical system 93 shown in FIG. 31. In this case, however, the number of constituent members of the optical system increases, and thus the cost increases. Moreover, the lens frame arrangement becomes complicated. Therefore, such an approach is unfavorable.
To construct a distortion-free optical system having a wide field angle and satisfactorily corrected for aberrations as an optical system for an image read apparatus, if a rotationally symmetric optical system is used, the number of lens constituent elements becomes undesirably large, and the resulting optical system inevitably becomes large in size and costly.
Another problem is concerned with mounting of an illumination system. When an illumination system is constructed by using a light source, e.g. an LED, to illuminate an information recording medium, illumination nonuniformity is likely to occur because it is necessary to dispose the illumination system in such a manner as to avoid a mechanical interference with a photographic optical system.
This problem arises from the fact that the arrangement of the optical system has an unfavorably low degree of freedom with regard to mounting. Therefore, the same problem may arise not only in pen-type information reproducing apparatuses but also in other forms of information reproducing systems.